Electrodynamic loudspeaker



Nov. 19, 1963 T. R. SCHOLL ELECTRODYNAMIC LOUDSPEAKER 2 Sheets-Sheet 1Filed Jan. 12, 1962 7050001?! A. JLI/Ull Nov. 19, 1963 T. R. scHoLLELECTRODYNAMIC LOUDSPEAKER 2 Sheets-Sheet 2 Filed Jan. 12, 1962 1NVENTOR.

7/11? 000! A. SCI/01 l wmwm floil ATTORNEYS United States Patent3,111,189 ELECTRODYNAMHC LGUDSPEAKER Theodore R. Scholl, 5007 47th NE.,Seattle, Wash. Filed Jan. 12, 1962, Ser. No. 165,741 21 Claims. (Cl.181-32) The present invention relates to electroacoustic devices, andmore particularly to dynamic loudspeakers of the socalled singlediaphragm type.

According to the present invention, a loudspeaker diaphragm isconfigured to be elongated in one face dimension and laterally inset atgenerally intermediate but somewhat off-center side portions so as toprovide a unique viol shaped diaphragm edge configuration providing aneffective piston area wherein the end areas are geometrically similarwith one somewhat larger than the other, the larger end areaconstituting a woofer zone, while the somewhat smaller end areaconstitutes a mid-range zone, and the relatively narrow or neckedconnecting area therebetween constitutes a tweeter zone, theconfiguration and construction of the tweeter zone accomplishing whatmay be termed dynamic decoupling between the woofer zone and mid-rangezone so that the speaker is essentially dynamically balanced even thoughsomewhat nonsymmetrical constructionally.

As a direct consequence and primary advantage of the loudspeakerdiaphragm configuration here presented, with varying radial dimensionsin the various woofer, midrange, and tweeter zones of the diaphragmpiston area, a wide and continuous range and spectrum of naturalfrequency modes are available, the lowest natural frequency mode of thediaphragm piston area being determined by the largest radial dimensionthereof in the woofer zone and the highest natural frequency mode of thediaphragm piston area being determined by the smallest radial dimensionof the tweeter zone piston area. To augment the dynamic separation ofthe woofer and mid-range zones, the wall of the tweeter zone isrelatively stiff, and the walls of the mid-range and woofer Zones areeach relatively less stifi". Thus, the relatively stiff tweeter zonesurrounding the diaphragm driving element serves to balance thevibration excursions of the diaphragm, since the primary ordominantimpedance of the diaphragm as seen by the motor element is that of thetweeter zone, so that whatever impedance unbalance arises from therelative difference in geometry of the woofer and mid-range zones doesnot materially unbalance the vibration excursions of the diaphragm.

It is also an important feature and characteristic of the unique speakerdiaphragm configuration of the pres .ent invention that the viol shapeedge configuration thereof is substantially the same shape as manyinstruments creating music reproduced by the speaker, and therefore hasa greater capability of achieving similar natural resonancecharacteristics.

Any imperfection in loudspeaker fidelity is most discernible when thesound being reproduced comprises music played by stringed musicalinstruments. Violin music is commonly and particularly notable in thisrespect in that its true tonal qualities are notoriously diiiicult toreproduce. The Viol-shaped speaker diaphragm here presented has aperiphery with a geometry quite similar to the resonance boxes ofstringed instruments of the viol family, and'therefore has a range andspectrum of nat ural resonance frequency modes functionally compara bleto that of the instruments themselves. The speaker of the presentinvention is thus ideally and uniquely configured for accurateelectroacoustic reproduction of music played by stringed instruments. Itis physically shaped like, and therefore geometrically tuned to suchinstruments, and the performance of the speaker in this respect isdemonstrably superior to conventional round or oval loudspeakers ofcomparable quality of construction.

Other objects, advantages and characteristics of the present inventioninclude; the provision in an electrodynamic loudspeaker of the singlediaphragm type of optional means to accentuate high frequencies bysurface coatings on all or part of the diaphragm piston area, such asurface coating preferably having particulate, crystalline materialtherein over certain portions of such diaphragm piston area; theprovision of optional diaphragm housing arrangements, certain of whichprovide a degree of control of rear air impedance so as to augment thehigh frequency performance characteristics of the tweeter zone portionof the diaphragm; provision of a single diaphragm loudspeaker designhaving essentially the frequency re sponse characteristics ofmultiple-speaker systems without the cost or complexity thereof; andprovision of extended range single diaphragm loudspeakers which can befabricated essentially as simply as and at essentially the same cost asconventional round or oval single diaphragm speakers of comparable size.

These and other inherent objects, features, advantages andcharacteristics of the present invention will be apparent from thefollowing discussion of certain typical and therefore non-limitativeembodiments thereof, taken together with the accompanying drawings,wherein like letters and numerals refer to like parts, and wherein:

FIG. 1 is a front face view of a loudspeaker according to the presentinvention;

FIG. 2 is a rear view of the speaker shown at FIG. 1;

FIG. 3 is a side view of the speaker shown at FIGS. 1 and 2;

FIG. 4 is a top view of the speaker shown at FIGS. 1-3;

FIG. 5 is a view in longitudinal cross section of the speaker shown atFIGS. 1-4, taken substantially along line 5-5 of FIG. 1;

FIG. 6 is a cross sectional view of the speaker shown at FIGS. 15 takensubstantially along line 6-6 of FIG. 1; and

FIG. 7 is a front face view of a somewhat modified form of loudspeakeraccording to the present invention, utilizing a non-symmetrical surfacecoating in predominantly the mid-range and tweeter zones of thediaphragm piston area, and further incorporating a tweeter zone radiatorat the diaphragm apex.

The permanent magnet type electrodynamic loudspeaker shown in FIGS. 1-6comprises a concave openfaced diaphragm collectively designated DW, DT,DM and a motor or driver element generally designated M, the diaphragmedge and motor M being structurally attached to a rear housing or frameH. The piston area of the diaphragm, collectively designated 10W, 10T,10M, includes a series of compliance or stiffening ribs 11 and is joinedby a flexible annulus 12 to a rigid housing edge 14 extending along theperiphery of the diaphragm, and a cushioning ring 16 is in turn attachedto the housing edge 14. Mounting holes, certain of which are indicatedat 18, are provided for mounting of the speaker in an enclosure or thelike in the usual manner.

Any desired number of compliance rings 11 and flexible annuli 12 can beprovided, the basic purpose of the latter being simply that of providinga relatively flexible decoupling between the piston area 10W, 10T, 10Mand the retained diaphragm peripheral edge. It is important, however,that the diaphragm wall be relatively more flexible inthe portionsthereof more remote from the diaphragm apex and be relatively stiff inthe portions thereof immediately around the diaphragm apex, i.e. in theportions thereof within the central diaphragm area DT, in order toenhance the dynamic decoupling of the diaphragm areas DW, DM, ashereinafter more fully discussed.

Diaphragm DW, DT, DM is suitably constituted of pressed paper stock orlike pliant material which without surface finish or stiffening coatingis relatively soft, and in the embodiment of the invention shown atFIGS. 16 the major portion of the diaphragm piston area 10W, 10T, 10Mout to the first compliance ring 11 is coated with a stiffening agentsuch as shellac, starch or the like, as. shown in FIG. 1 by lightstippling. Preferably, also, the immediate area surrounding thediaphragm apex, i.e. piston area portion 10T is more heavily coated withthe stiffening agent, as shown in FIG. 1 by heavy stippling, to augmenthigh frequency response and relatively increase the impedance of thecentral diaphragm area DT. In addition, it has been found advantageousfrom the point of view of increasing high frequency response to includein the stiffening coatings a particulate crystalline material such asburnt amber crystals.

As will be evident, a considerable latitude is available as to thearrangement of a stiffening coating in the various piston area portions10W, ltiT, 10M (noting FIG. 7 and the discussion thereof below, forexample) and it is a practical feature of the loudspeaker diaphragmconfigurations of the present invention that if in production a givenspeaker or speaker design evidences some dynamic unbalance or undesiredfrequency response pattern, such can be compensated for to aconsiderable degree simply by appropriate non-symmetrical application ofa stiffeningcoating to more nearly equalize the impedance of the pistonarea end portions 10W, 10M.

The construction and fabrication of the rear housing H can beaccomplished in any desired manner known per se, so long as at least themajor diaphragm piston area is suitably vented to reduce rear airimpedance, as by cutouts, open framing or vent holes of any desiredsize, such as the various vent holes provided in rear housing H andindicated in certain instances at 20. It has been found preferable,however, to provide a solid wall structure in the areas of housing Hdirectly to the rear of the central diaphragm area DT, to improve theimpedance and high frequency response thereof.

The speaker drive mechanism or motor M can suitably be a typeconventional per se, For example, as shown at FIG. 6, the motor M can beof the permanent magnet type, presenting a pole piece 22 to a so-calledmoving coil or voice coil 24 wound on a short sleeve 26 attached to theapex hole of the diaphragm, the vibration excursions of moving coil 24being transmitted through sleeve 26 to the diaphragm. A flexible annularspider 28 seals the motor M in the conventional manner. Also in a mannerconventional per se, a dome 30 caps the diaphragm opening around themoving coil 24 and pole piece 22. As will be understood, vibrationexcursions of sleeve 26 occur perpendicularly of the face plane of thespeaker (coincident with ring 14), in the same manner as characteristicof conventional electrodynamic loudspeakers.

Turning to a more specific consideration of the characteristicconfigurations of diaphragm DW, DT, DM and piston area 10W, 10T, 10M, itwill be seen from the accompanying illustrations the face configurationis characterized by: a lower (as shown), relatively wide, relativelylarge end area DW (with piston area 10W), constituting a woofer zone; anupper (as shown), somewhat less wide and somewhat lesser area endportion DM (with piston area 10M) constituting a mid-range zone; and anarrow, smaller area throat or necked portion DT (with piston area 10T),constituting a tweeter zone.

characteristically, also, the diaphragm and piston area configurationsare symmetrical laterally of the major axis of the speaker and somewhatnon-symmetrical along such major axis. This diaphragm configuration isdescribable simply as an elongated, centrally constricted sloped-walldiaphragm, with a major end lobe (DW) and a minor end lobe (DM) having arelatively constricted connecting portion (DT) therebetween, the majoraxis of the diaphragm face (section line 5') bisecting said lobes andthe diaphragm apex (with the motor element or moving coil 24) of thespeaker being situated so that the axis of movement thereof issubstantially perpendicular to and coincident with said major axissubstantially at the relatively constricted connecting portion betweenthe end lobes.

Considering the diaphragm configuration of the speaker shown at FIGS. l6in yet another aspect, the wall of the piston area 10W, 10M, NT is seento variously presentrelatively small acute angles with reference to thefiat face plane of the speaker where the radii of such piston area arerelatively long (10W, 10M) and present relatively large acute anglesthereto where the radii of such piston areas are relatively short (10T),with progressive and continuous intermediate variations in wall anglesand length of radii. Consequently a wide range and good spectrum ofnatural frequency modes are avail able, the shortest, lateral radii inthe piston area 101 of the tweeter zone being only about one-fifth (forexample) the length of the effective radii of the piston area ltiM ofthe mid-range zone, which are in turn about four-fifths (for example)the radial length of the opposite radii in the piston area 10W of thewoofer zone.

The relatively abrupt wall angles at the sides of the tweeter zone alsoserve the advantageous purpose of providing good lateral dispersal ofhigh frequencies.

The dominant impedance presented to the vibration excursions generatedby movement of moving coil 24 is that impedance generated by thestructural characteristics of the tweeter zone DT. As a consequence ofthis, the relatively lesser impedances characteristic of the midrangepiston area 10M and the woofer piston area 10W do not materiallymanifest any dynamic unbalance to the diaphragm as a whole even thoughthey may be somewhat unlike in impedance because of the non-symmetry ofthe speaker configuration along its major axis. The structuralnon-symmetry of the woofer and mid-range zones can thus be said to beessentially dynamically decoupled by the laterally narrow and relativelystiff tweeter zone therebetween.

The open-faced diaphragm edge configuration here presented is forsimplicity also describable as of vio shape, employing the term viol byanalogy to the usage thereof in the field of stringed instruments,wherein it denotes a type of instrument having a hollow resonance box orenclosure with a constricted or necked region separating two relativelylarge end regions which are geometrically similar, with one slightlylarger than the other.

FIG. 7 shows a somewhat modified form of speaker also characteristic ofthe invention, constructed and configured like that shown in FIGS. 1-6except that the piston area 10W, 10T, 10M has (as shown by stippling) astiffening coating applied thereto which extends over most of themid-range piston area 10M out to the first compliance ring 11 and overall of the tweeter piston area WT but not over the woofer piston area10W. Also, in a manner conventional per se, a conical dispersal cone orradiator 32 stands outwardly from the diaphragm apex, as by beingcemented to the edge of dome 30, to augment the relatively abrupt sidesof the tweeter zone in providing a good highs dispersion pattern. Asearlier discussed, the non-symmetrical stiffening coating, applied asshown in FIG. 7 to the tweeter zone and but one lobe of the diaphragm,increases the effective impedance of that lobe, while the non-stiffenedlarger lobe provides maximum lows response and the radiator 32 furtherextends the highs response.

To illustrate a typical dimensional pattern for a speaker according tothe present invention, the speaker shown at FIGS. 1-6 can have anoverall diaphragm area the same as a round conical speaker 15 in overalldiameter, the specific dimensions thereof measured edge to edge of thehousing frame being 19" along the major axis, 12" at the widest lateraldimension in the major lobe, 9" in the widest lateral dimension in theminor lobe, and 6.

across at the narrowmost lateral dimension, the cone depth from faceplane to apex being 1%, and the motor having a 2" voice coil and a 1-3lb. permanent magnet. The relatively quite shallow depth (1%") of thecone, along with commercially available shallow or inverted motor units,makes practicable the use of the speaker with quite thin enclosures, oras a built-in installation in a wall, for example. It will be of courseunderstood that the speaker can be any desired size so long as theessential viol shape edge configuration is preserved. As will also beapparent, any suitable type of motor or equivalent driver can be used.It is also possible to adapt the basic diaphragm configuration toexponential horn applications. Usage of various size speakers inconcert, all with a viol-shaped edge configuration, or with only a partof the speakers with a Viol-shaped edge configuration, are of coursealso readily possible.

From the foregoing, further diaphragm geometry and pattern variations,as well as various other constructional modes characteristic of thepresent invention will be apparent to those skilled in the art to whichthe invention is addressed, within the scope of the following claims.

What is claimed is:

1. An electrodynamic loudspeaker having an open diaphragm face slopingfrom a single apex to a planar edge of substantially viol shape.

2. An electrodynamic loudspeaker comprising an openfaced diaphragm witha. planar edge of essentially viol shape, the diaphragm apex area beingsubstantially between the laterally narrowmost edge portions of thediaphragm, and the said loudspeaker further comprising motor means indriving relation to said diaphragm apex area.

3. An extended range dynamic loudspeakercompr-ising a sloped-faceddiaphragm with a single diaphragm apex, a motor element coupled to thediaphragm apex, a rigid frame mounting said motor element and rigidlyretaining the edge of said diaphragm, the sloped-face configuration ofsaid diaphragm being characterized by a planar edge and by a wide,relatively large lower piston area and a somewhat less wide upper pistonarea with a smaller, relatively narrow intermediate piston areatherebetween, the diaphragm apex being in said intermediate piston areaand the said motor element being situated to directly drive said narrowintermediate piston area.

4. An extended range dynamic loudspeaker comprising an open-faceddiaphragm radiating from an apex occupied by a single motor element andhaving at least one compliance ring situated near the edge thereof,which edge is in turn affixed to a rigid frame through a flexibleannulus, the face configuration of the diaphragm being that of a largearea major lobe and a somewhat lesser area minor lobe with a relativelyconstricted lobe connecting area therebetween, the major axis of thediaphragm face bisecting said lobes, and the diaphragm apex beingsituated in said relatively constricted lobe connecting area.

5. An extended range dynamic loudspeaker comprising an open-faceddiaphragm with a motor element positioned at the diaphragm apex, saiddiaphragm being flexibly joined at its edge to a rigid frame extend-ingperipherally of the diaphragm, the face configuration of the diaphragmand frame being characterized by a wide, relatively large lower area anda somewhat less wide upper area with a relatively small and narrowintermediate area therebetween, the radial angles of the diaphragm wallwith respect to its face plane being substantially inversely related tothe corresponding radial dimensions thereof.

6. An electrodynamic loudspeaker having a sloped- Wall, open-faceddiaphragm of elongated and necked edge configuration, the necked portionof the diaphragm edge being situated somewhat non-symmetrically of theends thereof, with one end area of said diaphragm being slightly largerthan the other end area so that the larger 6 end area essentiallyprovides a woofer zone, the smaller end area essentially provides amid-range zone, and the necked diaphragm area therebetween essentiallyprovides a tweeter zone, all driven by a motor element situated in saidtweeter zone.

7. A loudspeaker according to claim 6, comprising a dispersal conesituated in said tweeter zone.

8. An extended range dynamic loudspeaker comprising a motor element andan open-faced sloped-wall diaphragm emanating therefrom to flexibleannulus means in turn attached to a rigid frame of essentiallyViol-shape, with the motor element situated at the laterally narrowmostportion of the diaphragm face, the piston area of the diaphragmpresenting relatively shallow angles with reference to the face plane ofthe loudspeaker where the radii of such piston area are relatively longand presenting relatively abrupt angles thereof where the radii of suchpiston area are relatively short.

9. A loudspeaker according to claim 8, wherein the piston area of saiddiaphragm is relatively flexible along the relatively large radiithereof, and relatively stiff along the relatively short radii thereof,so that the acoustic impedance of said piston area as seen by said motorelement is relatively high in the laterally narrowmost portion of thediaphragm face.

10. A loudspeaker according to claim 8, wherein said rigid frame is theedge of a diaphragm rear housing presenting an essentially solid formrearwardly of the relatively short radii portions of the diaphragm tomaintain the rear air impedance thereof relatively high, and presentinghousing openings rearwardly of the relatively long rad-ii portions ofthe diaphragm to maintain the rear air impedance thereof relatively low.

11. An extended range dynamic loudspeaker having a single motor elementand an elongated, shallowly openfaced, sloped-walled diaphragm radiatingtherefrom, the face configuration of said diaphragm being withrelatively large area laterally wide end portions and a relatively smallarea necked portion therebetween, one of said end portions beingrelatively larger than the other and constituting a woofer zone, theother said end area constituting a mid-range zone, and the necked,intermediate area therebetween constituting a tweeter zone, the saidmotor element being situated to directly drive said tweeter zone, theacoustic impedance presented to said motor element being predominantlythat of the necked portion of the diaphragm so that the loudspeaker isessentially dynamically balanced even though the end areas thereof arerelatively non-symmetrical.

12. A loudspeaker according to claim 11, wherein the piston area of saidtweeter zone is relatively stiff and the piston areas of said woofer andmid-range zones are each relatively less stiff so that high frequencyexcursions of the diaphragm are primarily confined to said tweeter areaand the mid-frequency and low frequency excursions thereof are primarilydeveloped in the mid-range and woofer piston areas, with a wide rangeand good spectrum of natural frequency modes, the lowest naturalfrequency mode of the diaphragm being determined by the largest radialdimension of the woofer zone piston area, and the highestnaturalfrequency mode of the diaphragm being determined by the smallestradial dimension of the tweeter zone piston area.

13. A loudspeaker according to claim 12, wherein the ratio of theshortest tweeter zone radius to the longest mid-range zone radius isabout 1:5 and the ratio of the longest mid-range zone radius to thelongest woofer zone radius is about 4:5.

14. A single cone, single motor element loudspeaker providing combinedwoofer, mid-range and tweeter response; said loudspeaker having anopen-faced, slopedwall type diaphragm with a face configurationinvolving wide, large area ends with a narrow, small area throat portiontherebetween, and a magnetic type motor means comprising a voice coilelement situated in said throat portion, such throat portion being ofrelatively stiff-wall construction and providing a tweeter zone, one ofthe end areas being somewhat-larger than the other and providing awoofer zone, and the smaller of the end areas providing a mid-rangezone, the stiff-walled tweeter zone construction establishing thedominant impedance presented to the motor element so that, the diaphragmis essentially dynamically balanced even though of somewhatnon-symmetrical configuration.

15. An electrodynamic loudspeaker having an openfaced. sloped-walldiaphragm of elongated and necked edge configuration bounded by a planarrigid frame and driven by a motor element situated at the diaphragmapex, the necked portion of the diaphragm being situated somewhatnon-symmetrically of the ends thereof along a major axis with one endarea being slightly larger than the other end area sov that the largerend area provides a woofer zone, the smaller end area provides amid-range zone, and the necked diaphragm area therebetween provides atweeter zone, with said diaphragm apex being situated in said tweeterzone; the said loudspeaker having substantially the following relativedimensions:

Dimension Dimensional units Major axis 19 Widest lateral dimension atwoofer zone l2 Widest lateral dimension at mid-range zone 9 Narrowestlateral dimension at tweeter zone 6 16. A loudspeaker according to claim15, wherein the depth of the diaphragm from the face plane thereof tothe diaphragm apex is about 1% dimensional units.

17. An electrodynamic loudspeaker of extended frequency response and a,wide range of natural frequency modes, comprising an open-faced,sloped-wall type diaphragm of pressed paper construction, driven by amotor means and, having a piston area configuration involving a largewoofer lobe and a somewhat smaller mid-range lobe, and with a neckedtweeter portion therebetween, the

' said motor means being connected to said diaphragm in said tweeterportion, and the said piston area having a stiffening coating on thecentral portion thereof, applied most heavily in said tweeter portion.

18. A loudspeaker according to claim 17, wherein said stiffening coatingincorporates crystalline particulate material to augment high frequencyresponse of the speaker.

19. A loudspeaker according to claim 18, wherein the crystallineparticulate material comprises burnt amber.

20. A loudspeaker according to claim 17, wherein said stiffening coatingis applied entirely over the said tweeter portion, and partly over saidmid-range portion, but not over said woofer portion of the diaphragmpiston area.

21. An electrodynamic loudspeaker comprising a motor element, a rigidframe, and a pliant, concavely open-faced diaphragm magnetically drivenby said motor element and edge joined to said frame along a fiat faceplane, the edge configuration of said diaphragm at its planar juncturewith said frame being of substantially viol shape, with the concave faceof said diaphragm being deepest substantially in the laterallynarrowmost portion thereof, and with the said motor element beingcoupled to said diaphragm at its deepest face portion.

References Citetl in the file of this patent UNITED STATES PATENTS1,689,136 Hastings Oct. 23, 1928 2,146,975 Nagelvoort Feb. 14, 19392,549,091 Hopkins Apr. 17, 1951 2,717,047 Buchmann Sept. 6, 19553,026,958 Haerther Mar, 27, 1962 FOREIGN PATENTS 176,098 Great BritainFeb. 27, 1922

1. AN ELECTRODYNAMIC LOUDSPEAKER HAVING AN OPEN DIAPHRAGM FACE SLOPINGFROM A SINGLE APEX TO A PLANAR EDGE OF SUBSTANTIALLY VIOL SHAPE.